Multifuel burner

ABSTRACT

A BURNER CAPABLE OF OPERATING ON A GASEOUS AND A LIQUID FUEL SEPARATELY AND IN COMBINATION WITH EACH OTHER TO PRODUCE A FLAME WHICH HAS A GREATER EXTENT IN LATERAL DIRECTIONS THAN IN AN AXIAL DIRECTION. A FLARED TUNNEL EXTENDS THROUGH A REFRACTORY WALL AND HAS ITS AXIS NORMAL TO THE INNER PLANAR SURFACE OF THE WALL. THE FLARED SECTION OF THE TUNNEL IS SYMMETRICAL IN LATERAL PLANES AND IS SMOOTHLY CONTOURED INTO THE INNER PLANAR SURFACE OF THE WALL. A CONICAL STREAM OF LIQUID FUEL PARTICLES IS INJECTED INTO THE SMALL END OF THE FLARED SECTION SO THAT ITS CONICAL ANGLE IS SUBSTANTIALLY TANGENT TO THE SURFACE OF THE MIDSECTION OF THE FLARED SECTION. SURROUNDING THE LIQUID FUEL SUPPLY TUBE IS A GASEOUS SUPPLY TUBE FOR SUPPLYING AN ANNULAR COLUMN OF GASEOUS FUEL TO THE ENTRANCE OF THE FLARED SECTION. MEANS ARE PROVIDED FOR SUPPLYING HELICALLY SWIRLING ANNULAR COLUMN OF COMBUSTION AIR ADJACENT THE TUNNEL SURFACE AROUND THE FUEL STREAM OR STREAMS.

June 20, 1972 J. CHEDAILLE ETAL MUL'BIFUEL BURNER 2 Sheets-Sheet 1 Filed March 30, 1970 Var June 20, 1972 J. CHEDAILLE ET AL MULTIFUEL BURNER 2 Sheets-Sheet 2 Filed March 50, 1970 United States Patent US. Cl. 431174 3 Claims ABSTRACT OF THE DISCLOSURE A burner capable of operating on a gaseous and a liquid fuel separately and in combination with each other to produce a flame which has a greater extent in lateral directions than in an axial direction. A flared tunnel extends through a refractory wall and has its axis normal to the inner planar surface of the wall. The flared section of the tunnel is symmetrical in lateral planes and is smoothly contoured into the inner planar surface of the wall. A conical stream of liquid fuel particles is injected into the small end of the flared section so that its conical angle is substantially tangent to the surface of the midsection of the flared section. Surrounding the liquid fuel supply tube is a gaseous supply tube for supplying an annular column of gaseous fuel to the entrance of the flared section. Means are provided for supplying a helically swirling annular column of combustion air adjacent the tunnel surface around the fuel stream or streams.

'FIELD OF INVENTION This invention relates to liquid fuel burners of the air swirl type wherein an auxiliary gaseous fuel may be used to enhance the combustion of the liquid fuel. It deals with a burner of this type which produces a flat flame in which combustion is already complete in a plane at right angles to the central burner axis and which is located at a short distance, for example about centimeters, downstream from the plane of the burner outlet for a burner of the size shown in the drawings. The lateral extent of the flame is substantially greater than 30 centimeters.

According to this invention, the burner is characterized by the fact that the liquid fuel tube with its discharge nozzle is coaxially arranged within an opening provided in a refractory wall of the enclosure to be heated, the internal end of the opening being outwardly flaring and joining up with the internal face of this wall, without forming a sharp edge, and in that the outlet ports of the nozzle are so directed as to have the fuel jets passing through these ports directed substantially tangential with respect to the flaring section of said opening, preferably in the median zone of said flaring section.

According to a preferred embodiment of this invention, the burner is of the multifuel type and includes, in addition to the liquid fuel injector tube, a concentrically disposed gaseous fuel inlet tube which terminates substantially at the beginning of the flaring section of the opening provided in the wall of the enclosure to be heated.

The above mentioned objects and advantages and other objects and advantages and the manner of attaining them will be apparent from the following description made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the burner along 1- 1 of FIG. 2.

FIG. 2 is a sectional view of the burner along 2-2 of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT -As shown in the drawings, the burner 10 includes a refractory wall member 12 of the enclosure to be heated. It may be located in the roof or any other section of the enclosure. The wall section 12 defines a tunnel extending laterally therethrough beginning with a cylindrical tunnel section 14 and terminating with an arcuately flared section 16 which is smoothly contoured into the adjacent planar inner surface of the wall member 12. The curve of the flare may have a radius R equivalent to between about 0.5 to 2.5 times the diameter d of the cylindrical or small end of the flared section 16. Preferably radius R is between about 1 to 2 times diameter d. Hyperbolic or other similar curves may also be used provided that the ratio between the diameters of the large and small ends of the flared section is suitably between about 1.521 and 3.511 or preferably between 2:1 and 3:1. The axial length of the flared section 16 is suitably equivalent to about 0.5 to 2.5 times the diameter of the small end of the flared section and preferably about 1 to 2 times the diameter.

Liquid fuel is supplied to the flared section 16 by means of a tube member 18 concentrically disposed in the cylindrical section 14 and terminating with a nozzle 20 adjacent the small end of flared section 16. The nozzle 20 is designed so as to at least partially atomize the liquid fuel and produce a hollow cone of liquid fuel particles. The conical angle is such that the conical stream is directed so as to substantially intersect tangentially a midsection of the flared section as shown in FIG. 1 of the drawings. To accomplish this the nozzle may have an annular slot or a series of ports arranged obliquely to the central axis of the burner so that the conical angle, i.e. the angle the fuel jets make with the central axis of the burner, is between about 35 and 55, for example.

Gaseous fuel is supplied to the entrance of the flared section 16 by a tube member 21 located concentrically in the cylindrical section 14 of the tunnel. The cylindrical gaseous fuel supply tube 21 has a diameter that is substantially larger than the outside diameter of the liquid fuel tube 18, but smaller than the inside diameter of the cylindrical tunnel section 12. Tube 22 terminates within about 1 diameter of the entrance of the flared section 16 upstream from the liquid fuel nozzle 20. Two annular chambers are formed by this arrangement. The inner chamber 22, that is the chamber formed between the outside of tube 18 and the inside of tube 21, is for supplying an annular column of gaseous fuel arround the liquid fuel. The outer chamber 23 formed between the outside of tube 21 and the inside of tunnel section 12 is for supplying a helically swirling annular column of combustion air to the flared section 16 on the outside of the liquid and gaseous fuel streams.

The tube members 18 and 21 are sufliciently long to extend beyond the outside of the enclosure wall whereat they have means for connecting their respective fuel transmission lines. An outer extension 24 is provided for the refractory tunnel. This extension is contained within a larger housing which forms a box 26 for the introduction of combustion air under pressure to the annular combustion air chamber. A swirling means, such as a plurality of tangentially directed inlet tubes 28, is provided at the upstream end of the chamber. The inlet tubes communicate between box 26 and the combustion air chamber. They may be arranged in a plane normal to the chamber axis and spaced around the axis at 90 intervals as shown in FIG. 2.

Upon operation, combustion air flows under pressure into the box 26 and then into the tube 24 through the inlet passages 28 which induce a swirl in the air flow. The air passes along the annular passage formed by the tubes 24 and 21 and discharges into the heating chamber through the tunnel in the enclosure wall. Due to its swirling movement, this air flows along the wall of the outwardly flaring section 16, forming on this wall a relatively thin stream. Part of this air flow turns back and engenders an annular swirl schematically represented by the arrows 30.

When the burner is operated on liquid fuels, for instance on light fuel-oil, on light fuel-oil combined with naphtha or reheated heavy fuel-oil, the jets of the vaporized steam/fuel or air/fuel mixture flow along the outwardly flaring section 16. Then they encounter the helically swirling annular air stream and mix with this air, combustion taking place downstream of the flaring section 16, along the inside face of the front wall 12. The thus produced flame is very widespread and homogeneous, so that the temperature over the inside face of the Wall 12 is very uniform; the difference between the extreme temperature points amounts to about 15 C. for various furnace temperature levels ranging from 900 to 1400 C. The longer the fuel jets remain in the air stream, the better the combustion. Experience has shown that this result is obtained when the said jets are substantially tangential to the median zone 32 of the outwardly flaring section 16.

Likewise, when the burner is operating on a gaseous fuel, the latter flows through the tube 21 and encounters the helically swirling annular air stream substantially in the median zone 32 of the outwardly flaring section 16; this gas is injected parallel to the central burner axis, but due to the annular swirl, the gas jet is opened out at the very moment it leaves the tube 21 and is directed towards the median zone 32. Here again, combustion takes place along the inside face of the wall 12 and the flame obtained is a widespread and short flame. It would be possible to have the tube 11 somewhat advanced or receded, but experience has shown that combustion is best when the internal end of the said tube is located substantially at the beginning of the outwardly flaring section 16.

It follows from the above description that the burner, according to this invention, is of the multifuel type in its preferred embodiment. -It is very easy to change over from a liquid fuel to a gaseous fuel, or vice versa, or use both fuels in combination without mechanical alteration or removal of the burner, but simply by opening or closing the fuel valves.

Also the burner, when operating on a given liquid or gaseous fuel, can be supplied either with cold air or with hot air. 'Flexibility in operation with cold air is such that at a given air supply pressure, the turndown ranges from 1 to 10 while still ensuring a complete combustion and without making it necessary to supply a higher air flow rate than that corresponding to the stoichiometric combustion of the fuel chose; with air at 300 to 500 C., the turndown range is of 1 to 5, also without air excess.

While the above description was made with reference to a specific embodiment of this invention, it is to be understood that it is meant to be illustrative only and not limiting in any sense except as defined by the appended claims.

We claim:

1. A burner capable of operating on gaseous fuel and liquid fuel separately or in combination with each other to produce a flame which has greater extent in a lateral direction than in an axial direction, said burner comprising: a refractory wall member having a planar inner surface and a tunnel extending laterally therethrough, said tunnel having an arcuately flared exit end section smoothly contoured into said inner surface, said flared section having an axial length equivalent to between 1 to 2 times the diameter of the small end thereof; a liquid fuel injection tube coaxially aligned with said tunnel; a fluid atomizing nozzle located at the discharge end of said tube adjacent the small end of said flared tunnel section to produce a hollow conical stream of atomized fluid directed so that its conical angle is substantially tangent to the surface of a median portion of said flared section; a gaseous fuel injection tube disposed concentrically with and spaced from said liquid fuel injection tube and said tunnel thereby defining two annular chambers, the inner chamber being for supplying gaseous fuel and the outer chamber being for supplying combustion air to said flared section;and means for supplying helically swirling combustion air in said outer chamber.

2. A burner according to claim 1 where in said flared section has a ratio between the diameters of its large and small ends of between about 2:1 and 3:1.

3. A burner according to claim 1 wherein the curve of the flare has a radius equivalent to about 1 to 2 times the diameter of the small end of the flared section.

References Cited UNITED STATES PATENTS 1,865,983 7/1932 Warner 43l-183 X 2,046,767 7/1936 Campbell 43l284 X 2,806,517 9/1957 Te Nuyl 431-483 3,042,105 7/1962 Bitterlich 43l-174 X CARROLL B. DORITY, JR., Primary Examiner US. Cl. X.R. 431-182, 284 

